1. Field of the Invention
The present invention relates to chiral ligands and transition metal complexes thereof that are useful in asymmetric reactions. More particularly, the present invention relates to chiral phospholanes, P,N ligands, N,N ligands, biphenols, and chelating phosphines and transition metal complexes thereof that are useful in asymmetric catalysis.
2. Description of the Prior Art
Discovery of new chiral ligands has been an essential element in the development of highly enantioselective transition metal-catalyzed reactions. New structural motifs play an important role in dictating enantioselectivities and reactivities of a reaction. With the growing demand of enantiomerically pure compounds in pharmaceutical and agrochemical industry, asymmetric catalysis has become increasingly more important because of its high efficiency.
For example, biaryl atropisomeric ligands have been explored as effective ligand scaffolds for many asymmetric transformations. One of the most frequently used chiral chelating phosphines is BINAP (Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345, Ohkuma, T.; Koizumi, M.; Doucet, H.; Pham, T.; Kozawa, M.; Murata, K.; Katayama, E.; Yokozawa, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 13529.).
Another family of excellent chiral phosphines is so called DuPhos (Burk, U.S. Pat. Nos. 5,329,015, 5,202,493, 5,329,015, Burk, M, J. J. Am. Chem. Soc. 1991, 113, 8518, Burk, M. J.; Feaster, J. E.; Nugent, W. A.; Harlow, R. L. J. Am. Chem. Soc. 1993, 115, 10125. Burk, M. J.; Wang, Y. M.; Lee, J. R. J. Am. Chem. Soc. 1996, 118, 5142), which has a rigid 1,2-bis(phosphino)benzene backbone and electron-donating phospholane groups.
Gladiali et al. (Gladiali, S.; Dore, A.; Fabbri, D.; Lucchi, O. D.; Manassero, M. Tetrahedron Asymmetry, 1994, 511.) made monodentate chiral phospholanes bearing the 1,1xe2x80x2-binaphthyl framework. However the method for their synthesis is not feasible to make the corresponding chelating chiral phospholanes. Stelzer et al. (Bitterer, F.; Herd, O.; Kuhnel, M.; Stelzer, O.; Weferling, N.; Sheldrick, W. S.; Hahu, J.; Nagel, S.; Rosch, N. Inorg. Chem. 1998, 37, 6408) only made racemic chelating phospholanes.
Reetz et al. prepared chelating chiral phosphinites using readily accessible binaphthanols as starting materials and demonstrated that they are excellent ligands for Rh-catalyzed asymmetric hydrogenation of dehydroaminoacids (Reetz, M. T.; Gosberg, A.; Goddard, R.; Kyung, S. J. Chem. Soc., Chem. Commun. 1998, 2077). John Brown made a chiral phosphine and pyridine ligand with a biaryl chirality. Several related chiral ligands are shown in the Figure below. 
While these ligands have been useful in a number of asymmetric reactions, there are still many more asymmetric transformations that can benefit from the discovery of new chiral ligands.
The present invention includes a ligand selected from the group consisting of compounds represented by A through K: 
herein the bridge group is selected from the group consisting of: (CH2)n wherein n is an integer ranging from 1 to 8, (CH2)nW(CH2)n wherein n and m are independently an integer ranging from 1 to 8 and W, wherein W is a divalent group selected from the group consisting of: 1,2-divalent phenyl, 2,2xe2x80x2-divalent 1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl, ferrocene, and a substituted derivative thereof; wherein each substituent in said substituted derivative is selected from the group consisting of: aryl, alkyl having 1-8 carbon atoms, F, Cl, Br, I, COOR, SO3R, PR3R2, OR, SR, PR2, AsR2, SbR2, aryloxyl, nitro, NR2, vinyl, substituted vinyl and a combination thereof, wherein each R is independently selected from the group consisting of: hydrogen, alkyl, aryl, alkaryl and aralkyl; wherein each X is independently selected from the group consisting of: hydrogen, halide, alkyl, aryl, alkoxy, silane, carboxylate and amide; each Y is independently selected from the group consisting of: hydrogen, alkyl, aryl, alkoxy, carboxylate and amide; and each Z is independently selected from the group consisting of: hydrogen, alkyl, aryl, alkoxy, amide, carboxylate, and a heterocyclic compound.
The present invention further includes a catalyst prepared by a process comprising contacting a transition metal salt, or a complex thereof, and a ligand selected from the group consisting of compounds represented by A through K as described above.
The present invention still further includes a process for preparation of an asymmetric compound using a catalyst according to the present invention. The process comprises contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst prepared by a process comprising contacting a transition metal salt, or a complex thereof, and a ligand selected from compounds represented by A through K as described above.
The ferrocene-based irridium (R,R)-f-binaphane complex reduces imines to the corresponding amines with 95-99.6% enantioselectivity and reduces xcex2-substituted-xcex1-arylenamides with 95% enantioselectivity.